1. Field of the Invention
The present invention involves a method that uses radiation and particularly solar energy or UV (photochemical) induced processes to convert derivatives of vegetable oils to useful products. In one embodiment, the invention provides a process for converting fatty acid esters or their derivatives to hydrocarbons such as alkenes, dienes, trienes and the like. In a more particular embodiment the invention relates to photochemical methods that convert long chain fatty acids to olefins, dienes and trienes that can, if necessary, be further refined, cracked, reformed or converted to vinyl monomers, halogenated hydrocarbons and other commercial products. In a still more particular embodiment, a method is provided for forming ketones (e.g., fatty ketones) and converting them to olefins by exposing them to radiation.
2. Background
Fossil fuels, specifically products refined from petroleum, remain the principal source of hydrocarbon feed stocks. In addition to being used as a source of gasoline and other fuels, said hydrocarbons are also converted, or used directly, to form the starting materials from whence most synthetically made plastics and commercial solvents are obtained. Thus critical monomers such as styrene, butadiene, acrylic acid, propylene, ethylene and tetrafluoroethylene are currently obtained as either direct cracking products of crude oil or derived from direct cracking products of crude oil. Critical solvents like naphtha, hexanes, petroleum ether, methylene chloride, chloroform, carbon tetrachloride and the like, also are all either directly obtained, or produced, from petroleum. As the supply of fossil fuels, particularly crude oil, dwindles, and as other nations in the world compete for the products derived from oil the costs of raw materials for commercial plastics will increase, supplies will become harder to get and fossil fuel sources will be unable to meet demand.
A series of reports document that a shortage of petroleum products as derived from fossil fuels is anticipated. (Nathan Lewis, Chemical Challenges in Renewable Energy, Cal Tech publication, 2004 incorporated, by this citation, herein). In anticipation of the expected shortages new sources of energy are continually being evaluated and proposed. This application focuses on another facet of the problem, namely, that new sources of raw hydrocarbon feedstocks alternative to petroleum must be developed. Though land is unlikely to have the potential of meeting the needs of the global energy demand through the production of biofuels because the area that would need to be cultivated for such purposes is nearly equivalent to the area now under cultivation world-wide, and biomass conversion to power isn't that efficient anyway (see Lewis, op cit), the use of biomass to produce the raw materials from whence plastics are derived is a much less imposing challenge, and obviously within reach of experimental developments in the chemical sciences using the sun.
A relatively few molecules produced by thermal decomposition (cracking) products of petroleum, unsaturated hydrocarbons mostly, form the basis of most of the commercial plastics industry. These include: ethylene (CH2═CH2), propylene (CH3CH═CH2), styrene (C6H5CH═CH2) and butadiene (CH2═CH—CH═CH2). Of these propylene is a particularly important starting material because it is used to form acrylic acid, the base stock of acrylates. Hydrocarbon solvents like petroleum ethers can be used directly from refined petroleum while halocarbon solvents like carbon tetrachloride (CCl4) and perchloroethylene (C2Cl4) are produced by halogenation of methane and ethylene respectively.
In a recent report (Aug. 22, 2005, Energy Futures: Trends, Outlook and Implications) Don McConnell, CEO Batelle Lab Operations said “Bio-based chemicals can provide a hedge to offset petroleum based polymers & “Bio-refineries” will first be developed from food processing capacity”. In accordance with one embodiment of this invention, the oils of common vegetable crops are an alternative potential source of critical monomers such as propylene, ethylene, butadiene, styrene and acrylic acid. Though none have been developed or exploited for same, certain vegetable crops contain percentages of oil ranging from a few percent for corn to almost 30% for crops like peanuts, and these oils, following chemical and photochemical change, are a source of hydrocarbon feed stocks. Major constituents of these oils are derived from glycerol (CH2OHCHOHCH2OH) in the form of long chain alkyl and alkenyl esters called glycerides. These are likely formed in nature, as they would be in the lab, by an esterification reaction involving reaction of a long alkyl or alkenyl chain carboxylic acid with glycerol. Said long chain fatty acids which include palmitic, stearic, oleic, linolenic and linoleic (and all of the acids derived from food oils—Table 12-2, C. R. Noller, Organic Chemistry, Saunders, 1965, page 209) are themselves, just one step removed from the raw materials of petroleum.
It has long been known that the oils and fats can be removed from the vegetable by extraction with hydrocarbon solvents such as hexanes or petroleum ether, processed and converted to products that can be used in foods such as cooking oils, tofu and the like. However most grower's organizations, for example the soybean growers association, corn growers association, peanut growers association, etc. clearly recognize they could find additional, uses of their crops in the industrial market and have efforts that are more or less active to develop alternative (sic industrial, as opposed to food) uses of their crops. Among the largest potential of these is the formation from soya oil of a fuel known as Biodiesel. Biodiesel is defined as mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats that conform to ASTM D6751 specifications for use in diesel engines. These mono-alkyl esters are mostly methyl esters that are made from the glycerides by trans-esterification—the process of cooking the glycerides in the presence of a catalyst with an excess of a low molecular weight alcohol, for example methyl alcohol. This produces glycerol as a side product which must be separated. Biodiesel refers to the pure fuel before blending with diesel fuel. Biodiesel blends are denoted as, “BXX” with “XX” representing the percentage of biodiesel contained in the blend (ie: B20 is 20% biodiesel, 80% petroleum diesel). In 2004, approximately 20 million gallons of biodiesel was produced by a group of processors. This is far from capacity and expected to grow. Biodiesel is made entirely from soy and its chemical composition is said to be in the form of the methyl esters of soy: (Source: National Biodiesel Board).
The essential fatty acids that are converted to methyl esters in the formation of Biodiesel are mainly the acids palmitic, stearic, oleic, linoleic and linolenic which are, in turn, the principle fatty acids found in most foodstuffs. Palmitic and stearic acid are the so-called “saturated acids” in that they are comprised of long hydrocarbon chains of 15 and 17 carbons containing no double bonds. Saturated fatty acid esters are disadvantageous in foods so a number of growers organizations have attempted to reduce their content in commercially grown crops either by genetically engineering seeds to produce lower amounts of saturated oils, or by finding growing regions that already produce lower amounts of saturated oils and increasing production in these areas. Oleic, linoleic and linolenic acid, as well as others, are unsaturated acids and therefore preferred in foods with oleic acid being particularly preferred. Typically, in the oil of soy, saturated acids make up from 10 to 20% of the mono, di- and tri-glyceride content while the remainder is a combination of 3 or more unsaturated acid glycerides.
The average molecular weight of soybean oil methyl esters is 292.2. This was calculated using the average fatty acid distribution for soybean methyl esters below.
Typical Soybean Oil Methyl Ester ProfileFattyPer-Acid centWt.FormulaPalmitic12.0270.46C15H31CO2CH3Stearic 5.0298.52C17H35CO2CH3Oleic25.0296.50C17H33CO2CH3Linoleic52.0294.48 CH3(CH2)4CH═CHCH2CH═CH(CH2)7CO2CH3 Lino- 6.0292.46CH3(CH2CH═CH)3(CH2)7CO2CH3lenic
Fatty acids themselves may be converted by chemical reaction to polymerizable monomers. An oxidized form of soya oil, so-called epoxidized soya oil, is used as an additive in monomer mixtures from whence plastic coatings are made and formed. Polyesters are also derived from dicarboxylic acids such as those that might be obtained from fatty acid feedstocks.